【java】114. Flatten Binary Tree to Linked List

问题原文https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list/description/

方法：递归

public void flatten(TreeNode root) {
        if(root == null) return;
        TreeNode left = root.left;
        TreeNode right =root.right;
        flatten(left);
        flatten(right);
        root.left = null;
        if(left == null && right == null) return;
        if(left == null) {
        	root.right = right;
        	return;
        }
        if(right == null) {
        	root.right = left;
        	return;
        }
        TreeNode current = left;
        while(current.right!=null) {
        	current = current.right;
        }
        current.right = right;
        root.right = left;
    }